An old friend of mine dropped some knowledge the other day. Here is what she said:
"My theory is: you should never get to the point of having to throw your shoes away because a) they have a soul (I know, debatable!:-)) b) it is a lost investment and you'd bear opportunity costs -> therefore, buy many shoes, wear each pair only sometimes, so that you'll never overuse them -> with the time they'll become vintage, and you'll still be able to resell them, maybe at an even higher price than the original one (if you're clever you'll find bargains!) -> have some cash coming in for further investment!"
Thank you for sharing your wisdom Flo ;P!